Before deciding to buy the Uno R4 I searched the web to see if OTA upload is supported, and from the forum posts here I got the impression that it was broken. I decided to take a chance anyway, and I'm happy to report that it's working fine, provided you declare a cloud variable. If you don't declare a variable then OTA upload will fail with the error: Binary not received by the board: board not found. Also, it wasn't clear from the guides that I read that you need to upload a cloud-compatible sketch so the board has the information it needs to connect wirelessly. I've only had the Uno for a few hours. I hope this helps someone google searching in the future!
EDIT: OTA upload also requires an "entry" level IoT Cloud subscription, which is inexpensive for the features available, in my opinion.